This invention relates to fuel additives and more particularly to diesel fuel additives which inhibit the polymerization of fuel components, the growth of bacteria in stored fuel, and corrosion inside the fuel tank.
With the increasing prevalence of standby power generation equipment for essential services, including hospitals, communication equipment and the like, it has become increasingly important to protect the fuel from degradation when stored for long periods of time. More recently, many of these standby motor generator systems have employed diesel engines making the stability of stored fuel an even more important consideration. Distillate fuels in general and diesel fuel in particular are prone with prolonged storage to form polymerizates which agglomerate into what is referred to as sludge which can clog fuel lines and fuel injectors preventing the reliable operation of the engine. In addition, water in the fuel and in the form of condensates in a partially filled storage tank will attack the metal of the tank forming rust which also promotes the polymerization of components in the fuel.
In addition, new regulations promulgated by the Environmental Protection Agency have recognized the problem of rusting tanks and require measures to prevent contamination of ground water which can occur from fuel leaking underground from rust perforated tanks.
Likewise, sludge formation can be accelerated by the growth of bacteria in the fuel.
Therefore, modern inhibitors should have the following characteristics in use.
The material should be a sludge dispersant. It is known that the deterioration of fuel oils involves polymerization reactions resulting in the agglomeration of macroscopic polymerizates into sludge. Although this reaction may be initiated by oxygen, additives containing antioxidants, such as hindered phenols or diamines of the types used in gasolines as gum inhibitors, are not totally effective for the purpose of preventing the polymerization mechanisms. The additive materials should also have rust-preventive properties. The additive materials should also be effective when the fuels are stored in the presence of metals and water and rust. The additive materials should also inhibit the propagation of bacteria.
The kinds of bacteria that grow in stored fuels thrive on nitrogen, sulfur, and phosphorus, as well as iron, generally in the form of its oxides. Bacterial growth can be reduced, if not eliminated, by employing the following preventive measures. A biocide should be employed. Of course, the elimination of materials in the fuel tank that contain nitrogen, sulfur or phosphorus would be helpful. Since the latter measure is practically impossible, these materials must be considered in the formulation of any additive. In addition, it is important to keep the fuel tanks clean and dry, in order to reduce or eliminate rust formation in the tanks.
Two standard test methods have been used as the best yardstick of an inhibitor's usefulness in prolonging fuel storage life. The first test is a variation of the color-stability test in Federal Specification VV-K-211 Kerosene. In addition to observing the color change, the amount of filterable sludge and sediment is also measured. The second test is a prolonged version of the Gulf Oil Company's Fuel Corrosion of Steel Test. The Bell Laboratories' version of these tests have been correlated against fuels actually stored in a stand-by power fuel tank. The first test is run at 210.degree. F. until an observable amount of sludge has formed. This test is essentially an accelerated heat-stability test and is run in the absence of water. The second test is run at 120.degree. F. over water in the presence of 1020 steel strip. This test is concluded after 12 weeks or when an observable quantity of rust and sludge has been deposited.
The accelerated heat-stability test is comparatively quick and useful for screening out the poorer additives; but because water is absent from this test, it is not capable of differentiating between those additives that are either ineffective rust inhibitors, or incapable of protecting the fuels when stored in contact with water and steel, and those that are effective under such storage conditions. It is precisely these conditions that are of importance since stand-by fuels are frequently in contact with metal and condensate water, and rusting may be often as severe a problem as sludge formation. A 12-week stability-and-rust test was designed to evaluate these effects.
Because of the importance of stabilizing the fuels for extended periods of up to 10 years with the fuels in contact with metal and water, it is also important that the additive exhibit properties which would enable it to be used as a reinhibitor and depolymerizer during its repeated use over prolonged periods of time.
The major oil companies and chemical manufacturers have provided a wide variety of inhibitors. Exemplary of the types of materials available are the following:
(1) nitrogen-containing, surface-active polymers such as duPont FOA-11 and duPont FOA-208.
(2) organic-soluble, surface-active, oxygenated amine such as Enjay Paradyne HO4. This product may also contain a minor amount of a polymeric dispersant.
(3) anionic fuel additives such as Apollo SDI-2R, a proprietary sludge inhibitor and dispersant as well as rust preventive, manufactured by Apollo Chemical Corporation.
(4) chelating-type metal deactivator such as an 80% solution of N,N'disalicylidene-1-2propanediamine in aromatic solvents.
(5) A film-forming metal deactivator such as Vanlube 601, R. T. Vanderbilt Company.
(6) an antioxidant such as 2,6 ditertiarybutyle-4-methylphenol provided in Enjay Parabar 441, and also, duPont A029.
To varying degrees, these materials alone or in various combinations have in the past provided some measure of protection for stored fuel with respect to some of the major properties required.
For very long term storage however, it is essential that the inhibitor employed be capable of being employed during routine maintenance to depolymerize and disperse the sludge that is inevitably formed.
It is also important that attempts to eliminate the problem of injector clogging at low temperature by the build up of hydrocarbon waxes in the fuel does not compound injector scoring problems by reducing or eliminating the lubricity of the fuel. It is therefore an objective of the present invention to provide a diesel fuel additive which inhibits the formation of sludge, and bacteria, in the fuel during long periods of storage. It is a further objective of the present invention to provide a fuel additive which inhibits the formation of rust in diesel fuel storage tanks.
It is yet another objective of the present invention to provide a fuel additive composition which is capable of depolymerizing and dispersing sludge and sludge forming polymers in diesel fuel and kerosene stored for long periods of time.